Proportion of Cytotoxic Peripheral Blood Natural Killer Cells and T-Cell Large Granular Lymphocytes in Recurrent Miscarriage and Repeated Implantation Failure: Case-Control Study and Meta-analysis

We aimed to compare the proportion of peripheral blood natural killer (NK) cells (CD3(-)CD56(+)) and T-cell large granular lymphocytes (CD8(+)CD57(+)) during preconception in a homogenous group of women with unexplained well-defined recurrent miscarriage (RM) and repeated implantation failure (RIF) vs healthy controls in relation to pregnancy outcomes. This case-control study followed by a literature review and meta-analysis was conducted in three university hospitals. Patients and controls were consecutively recruited from December 2015 to October 2017. In total, 115 women were included in the study: 54 with RM, 41 with RIF and 20 healthy controls with ae<yen> 2 term births. Percentages of CD3(-)CD56(+) and CD8(+)CD57(+) cells and sub-populations of CD3(-)CD56(+) cells did not differ between cases and controls. The results for women with subsequent miscarriage did not differ from those with live births. The meta-analysis of the literature showed higher NK-cell proportions in RM [mean difference 3.47 (95% CI 2.94-4.00); p < 0.001] and RIF [mean difference 1.64 (95% CI 0.82-2.45); p < 0.001] than controls. However, the heterogeneity between the different studies was high. The proportion of peripheral blood CD3(-)CD56(+) and CD8(+)CD57(+) cells in the preconception period does not reflect the risk of implantation failure or miscarriage and should not be recommended indicators for the management of RM and RIF. Further prospective large studies are needed to develop a reliable peripheral blood marker of immune deregulation.